The difference between Christianity and Zen Buddhism for me when I was in my twenties was that the basis of Christianity seemed to rest mainly upon the impossible belief that the dead body of Jesus after he was laid in the tomb somehow was reanimated and became immortal.
Zen Buddhism in this regard was much easier: What is immortal is spirit—never the flesh since it is composite and a dependent origination. This view appeared to chime with the other Christian view that Jesus was put to death in the flesh and made alive in the spirit (1 Peter 3:18).
Unfortunately, the bulk of Christians take what can only be described as the implausible view, i.e., the resurrection of the flesh. Buddhism takes the plausible view as did another kind of Christianity believing that spirit is immortal.
“Whoever sows to please their flesh, from the flesh will reap destruction; whoever sows to please the Spirit, from the Spirit will reap eternal life” (Galatians 6:8).
Wrongly taking up and defending the implausible view Christianity became an unsystematic religion unlike Buddhism. Whereas the practice of Buddhism consist in penetrating through and superseding the world of flesh until the questing spirit passes into the realm of pure spirit (the awakening), Christianity falls prey to the flesh. It is almost as if it wants the flesh to turn, magically, into spirit having all of its benefits with none of the shortcomings attributed to the world of flesh such as the fact that flesh cannot inherit the kingdom of God (1 Corinthians 15:50). This is the mindset of wanting to have your cake and eat it too.
Christianity certainly had to potential to be great, to be the younger brother of Buddhism. But instead, it turned into something convoluted and certainly unsystematic. Because of this, those former Christians who decide to examine Buddhism are certainly confused and will not likely succeed in Buddhism.
The good news, Christianity can be rebuilt to be systematic and spiritual. But, seriously, it ain’t going to happen; not because it is difficult but because Christians still think about how to gratify the desires of the flesh. These Christians will fight a protracted war against those who champion spirit just as the materialists of this age wage war against life, itself, that is, the animative principle (ātman) that is immortal and prior to all conditionality.